The assault happened sometime between midnight and 1.45am on Saturday (April 1) in the wooded area between George Street and Cottingham Road.
A police spokesman said: “The victim, who was in his 30s, suffered a cut to the head which required medical treatment.”
Witnesses or anyone with information about the attack are asked to contact Northamptonshire Police on 101 or Crimestoppers on 0800 555111.